High density enclosure for optical modules

ABSTRACT

Rack mountable equipment enclosures have been developed that contain a multiplicity of fiber optical component such as optical taps, arrayed waveguide gratings (AWGs), optical splitters, and optical switches at a greater component density than has been previously achieved. For example, 192 fiber optical taps can be contained in a standard 19 inch wide equipment enclosure that is only 1 Rack Unit (1.75 inches) high. This high component density is achieved by locating the optical components within a multiplicity of modular containers inside of the equipment enclosure. The components are connected to fiber optic pig-tails that extend beyond the modular containers. These pig-tails are terminated with multi-fiber connectors that are mounted on the front panel of the equipment enclosure. This strategy allows for efficient packing of the modular containers containing optical components in the full volume of the rack space that is available to the equipment enclosure.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/854,402 filed Apr. 22, 2013, the contents ofwhich are hereby incorporated by reference herein.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to packaging of fiber optic components(including taps, splitters, arrayed waveguide gratings, and switches)with high packing densities in order to fit a large number of componentsinto an enclosure that will occupy a minimum space in equipment racksthat are used in support of various types of fiber optic communicationsystems.

BACKGROUND OF INVENTION

Terrestrial communications throughout the world has grown to relyheavily on optical fiber communications technology. And there is anincreasing flow of signaling information that requires use of multipleoptical fibers in communication links from one point to another. Thevarious origination, termination, and relay points for optical fiberdistribution systems form huge matrices—much more complicated than, say,a map of the railroads or the electrical power grid infrastructures inthe United States and abroad. In fact, some optical fiber links do runalong power lines and railroad right-of-ways. But, they also run underseas, across farmers' fields, down city streets, into campuses andwithin buildings and homes.

Management of complex fiber optic communication systems requires manydifferent types of specialized optical and electronic equipment toensure that correct signals are continuously being sent and receivedwith minimum interruptions and that any failures are detected andquickly rectified.

At a very basic level, it is necessary to use an optical tap to extracta portion of the optical signal in each fiber within a transmissioncable so that its functionality can be monitored. In some cases,monitoring the total optical power level is sufficient. In other caseswhere multiple optical channels are simultaneously transmitted on asingle fiber using wavelength division multiplexing (WDM), it is oftennecessary to use arrayed waveguide gratings (AWGs) to separate theindividual optical channels before they are directed to monitoringequipment. In other cases, optical splitters and optical switches arealso employed for monitoring purposes. Due to the large number ofoptical fibers used in modern optical communication systems, manyoptical taps, AWGs, splitters and switches are employed. A multiplicityof these components is typically located inside of an equipmentenclosure and these enclosures are mounted in racks that fill equipmentbays.

Clearly, it is desirable to reduce both the size and expense of thevarious pieces of equipment required to accomplish the desiredmonitoring functions. And this has been an ongoing evolutionary processfor all types of equipment used in modern fiber optical communicationsystems.

The present approach for packaging various optical components likeoptical taps is to pack some manageable number of them into a containercalled a cassette that has optical connectors on one or more of itsnarrow sides. (See for example, “AFL Fiber Inside Plant—Xpress FiberManagement (XFM) Optical Cassettes”—www.AFLglobal.com.) These cassettesare, in turn, closely packed side-by-side into an equipment enclosurethat is mounted in an equipment rack such that most or all of theoptical connectors on the cassettes face outward for convenient access.(See “Fiber Enclosures: Rack-Mount Enclosure Selection Guide” by LevitonNetwork Solutions, 2222-222^(nd) Street, S.E., Bothell, Wash.98021—www.levition.com.) A 19 inch wide equipment enclosure wouldtypically hold ten or twelve side-by-side cassettes.

The LGX equipment design was originally developed by Lucent Technologies(now known as Alcatel-Lucent) but is now broadly used as a defactostandard in the fiber optical communications industry. A number of wellknow companies including ADC Telecommunications (See “LGX-Compatible(LSX) Preteminated Termination/Splice Panel With Pigtails—User Manual2009” ADC Telecommunications, Inc, P.O. Box, 1101, Minneapolis, Minn.55440-1101), Tyco Electronics, and Leviton (See “Fiber Enclosures:Rack-Mount Enclosure Selection Guide” by Leviton Network Solutions,2222-222^(nd) Street, S.E., Bothell, Wash. 98021—www.leviton.com) aresuppliers of the LGX racks, equipment enclosures, and cassettes. Somecompanies, like Net Optics and MiMetrix Technologies use proprietaryequipment enclosure designs for optical taps, but their overall topologyis similar to the LGX standard with cassettes that fit into closelyspaced openings on the front panel of a rack mounted equipmentenclosure. For example, one specific design offered by Net Optics (“FlexTap Data Sheet” by Net Optics, 5303 Betsy Ross Drive; Santa Clara,Calif. 95054—www.netoptics.com) has a total of 24 side-by-side cassetteseach containing two optical taps for a total of 48 taps that areterminated with optical connectors that fits into a standard 19 inchwide rack mounted equipment enclosure that is 1 RU high. (Note: 1 RUcorresponds to one unit of rack space that is 1.75 inches high. Typicalequipment racks have a total height of 42 RUs or 73.5 inches.) Thepackaging of optical taps provided by MiMetrix Technologies (“OpticalTap Data Sheet” by MiMetrix Technologies, 11160 C1 South Lake Drive,Suite 190; Reston, Va. 20191—www.mimetrix.com) has a higher densitybecause their design includes twelve optical taps each inside of 8cassettes whose optical connectors face outward on the front of anequipment enclosure that also has a height of 1 RU. The higher densityof optical taps offered by MiMetrix Technologies, 96 taps per 1 RU(8×12=96), is generally considered a more desirable feature than thelower density (48 taps per 1 RU) offered by Net Optics.

Finally, it would be advantageous if the density of various types ofoptical components like optical taps, AWGs and splitters could befurther increased so that less space would be consumed in equipmentbays. This is especially relevant for any equipment used in remotemonitoring stations because space there is particularly expensive toacquire and maintain.

Also see U.S. Pat. Nos. 5,363,465, 7,218,828, 7,853,112, 7,912,336,7,939,962, 8,180,192, 8,254,741, and U.S. Patent Application PublicationNo. 2010/0142907.

BRIEF SUMMARY OF THE INVENTION

The purpose of this disclosure is to describe an entirely new strategyfor increasing the packaging density of various optical components in anequipment enclosure. As a starting point, it is recognized that thepackaging density using the LGX enclosures, or any of the existingproprietary enclosures that are similar, is limited by the number ofmodular containers that can be packed closely together along the frontpanel of a rack mounted enclosure with their integral optical connectorsfacing outward. Since the maximum depth dimension of a typical modularcontainer is only a fraction of the depth permitted by an equipmentrack, there is normally a considerable amount of empty space behind themodular containers that is not utilized. For example, an LGX modularcontainer has a depth of approximately 5 to 10 inches (127 to 254 mm)while the depth of the equipment rack may be 20 inches or more.(Standard equipment racks are 19 inches wide and other non-standardracks are 21 and 23 inches wide, but there is no standard for theirdepth. However, the most commonly used depths are 23.6 inches, 31.5inches and 39.4 inches, corresponding to 60, 80, and 100 cmrespectively.) If this empty space could be beneficially occupied byadditional optical components, then the component density (per RU) couldbe increased beyond the limitations of the present equipment enclosuredesigns.

This strategy can be achieved by filling the entire 3-dimension rackspace allowed per RU with modular containers that do not have opticalconnectors mounted on their outer surfaces. Rather the opticalcomponents in the modular containers are connected to multi-fiber ribboncables that pass directly through small holes in the outer walls of themodular containers and continue on to terminate with optical connectorsmounted on the front panel of the equipment enclosure.

Basically, the optical component density using the LGX standard andrelated proprietary equipment enclosures designs is limited to a1-dimensional array of cassettes that must be so positioned to provideaccess to their surface mounted connectors. Any remaining space behindthese cassettes in the equipment rack can not be utilized. In contrast,use of optical fiber ribbon cables as “pig-tails” from the modularcontainers to the front panel allow these containers to located anywherein the 3-dimension volume of the rack space that is available for theequipment enclosure.

The new design employing fiber ribbon cables to connect opticalcomponents to the front panel of an equipment enclosure has beendesignated HDP for High Density Platform. As an example of its very highdensity performance, 192 optical taps can be contained in a single HDPenclosure that is only 1 RU (1.75 inches) high and 20 inches deep. Thisrepresents a two-fold improvement in density over MiMetrix Technologiesunit, discussed above and a four-fold improvement in density over theunit offered by Net Optics. Similar enclosures with depths in the rangeof 19 to 22 would have similar properties. Another example is anequipment enclosure also 1 RU high with a nominal 13 inch depth (in therange of 12 to 14 inches) that is used for applications where the rackdepth is limited by physical constraints and a smaller quantity ofsplitters is acceptable. Typically, this 13 inch depth enclosure housesone half the number of splitters of the 20 inch depth unit. There isalso a nominal 10 inch depth equipment enclosure, ranging from 9 to 11inches, that is specifically for PON (passive optical network)applications where the enclosure is placed in PON distribution cabinetsor in multiple dwelling units (with more restrictive depths than typicalequipment racks) for distribution to individual clients. These wouldnormally house a single or multiple(s) of 1×16, 1×32 or 1×64 planarlightwave circuit (PLC) splitters. (See “Planar lightwave circuitdevices for optical communications present and future” by HiroshiTakahashi et al, Proceedings of the SPIE, Vol. 5246 (2003) pp 520-530.)The PON enclosures are designed to be rack mounted or wall mounted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. FIG. 1 shows a planar lightwave circuit (PLC) for a single 1×2optical splitter assembled with one input fiber and two exiting fibers.When used as an optical tap, one of the two exiting fibers is designatedas the output fiber and the other is designated as the tap fiber.

FIG. 2. FIG. 2 shows a modular container that holds four optical tapssimilar to the one shown in FIG. 1. The input and output fibers fromtheses taps are organized within the container so that the four inputfibers are incorporated into a first optical fiber ribbon cable, thefour output fibers are incorporated into a second fiber ribbon cable,and the four tap fibers are incorporated into a third fiber ribboncable. The three fiber ribbon cables pass through holes in the wall ofthe modular container and are secured in place at the wall penetrationswith a bonding agent. These cables are often referred to as “pig-tails”because they are quite flexible and extend a considerable distance fromthe module before they are terminated with a multi-fiber connector suchas a standard MTP or MPO connector. (See, for example, “The MTPConnector, AEN 90, Revision 1-2002” by Corning Cable Systems, 800 17htStreet, Hickory, N.C. 28603-0489 and “Optical fiber connector”Wikipedia.)

FIG. 3. FIG. 3 is another example of a modular container that holds a1×32 optical fiber splitter. In this case, there is a single input fiberand four output ribbon cables that contain 8 fiber each, for a total of32 output fibers. This is a good example where both single fiber cableand multi-fiber cables are used.

FIGS. 4A, B, and C. FIG. 4A, FIG. 4B, and FIG. 4C show an exploded view,front view and back assembled views of a HDP equipment enclosure,respectively, that holds 16 modular containers similar to the ones shownin FIG. 2 and/or FIG. 3. The outside dimensions of most modularcontainers are approximately 3 inches by 5 inches by ½ inch which is aconvenient size for placing into the equipment enclosure that can berack mounted. If each modular container held 8 optical taps and all ofthe optical fiber ribbon cables terminated on the front panel using 8fibers in a multi-fiber connector such as MTP or MPO connector, thisequipment enclosure would contain a total of 128 optical taps(16×8=128). The density of optical taps could be increased to 192 byincreasing the number of taps in each modular container to 12 andemploying ribbon cables and associated MTP or MPO connectors having 12fibers each. This represents a practical arrangement.

FIG. 5. FIG. 5 shows how some of the optical fiber ribbon cables arepositioned within the HDP equipment enclosure. The reason that theseparticular ribbon cables follow an indirect loop path is explained belowin the Detailed Description of Preferred Embodiments.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the attached drawings, embodiments of the presentinvention will be described below.

FIG. 1 shows the basic construction of a typical optical tap made usingplanar lightwave circuit (PLC) technology. The optical circuit is formedon substrate 1 that is a polished wafer of pure fused silica or a waferof semiconductor silicon covered on its top side with the deposition ofa relatively thick layer of pure silicon dioxide (SiO₂) that isapproximately 20 microns thick. On the very top of substrate 1 there isa second deposited layer of doped silica glass that is approximately 7microns thick that has been patterned using techniques similar tosemiconductor processing. The refractive index of this deposited layeris approximately 0.3% greater than that of pure fused silica. In thecase of the optical tap, after processing, the remaining doped layer ofsilica glass has been reduced to a relatively simple “Y” shape 2 asshown in FIG. 1. This serves as a planar optical waveguide that dividesthe optical beam coming out of the input fiber 3 into two parts that aredirected to exiting fibers 4 and 5. In most practical applications, allof these fibers are single-mode fibers. Depending on the specificgeometry of the “Y” shape 2, the splitting ratio may be adjusted toachieve a splitting ratio of 50%-50% or some other values, like 90%-10%or 80%-20%. Normally, the output fiber 4 is the one that receives thegreatest optical power after splitting and the tap fiber is the one thatreceives the least optical power. In the special case of a 50%-50% splitin power, the designation of the output and tap fibers is arbitrary. Theleft and right side of substrate 1 usually includes “V” grooved channels(not shown) that help to align the centers of the input and exitingfibers to the center line of the planar “Y” shaped optical waveguide 2.The final step in making an optical tap like the one shown in FIG. 1 isusually to cover the substrate 1 and optical fibers 3, 4, and 5 withsecond thin wafer of pure fused silica (not shown) that is bonded inplace using transparent optical cement that is matched in refractiveindex to that of pure fused silica. For extra mechanical strength anddurability, the optical tap is usually enclosed in a metal package 6with open ends or holes to pass the optical fibers. This optical tapassembly is then an example of one of the various optical componentsthat can be included either singly or in multiplicity inside of amodular container, as shown in the next figure.

FIG. 2. shows an example of a modular container 7 that encloses fouroptical taps 6 a, 6 b, 6 c, and 6 d similar to the one shown in FIG. 1.Each optical tap is secured in place on the inner surface of a modularcontainer 7 with a boding agent such as a low stress epoxy cement toprevent undesired motion. The four input fibers 3 a, 3 b, 3 c and 3 d tothese taps are “fanned out” from a multi-fiber ribbon cable (pig-tail)30 that loops around inside of the modular container before exiting thecontainer through hole 8 c. Similarly, output fibers 4 a, 4 b, 4 c, and4 d and tap fibers 5 a, 5 b, 5 c, and 5 d are brought together inmulti-fiber ribbon cables (pig-tails) 40 and 50, respectively, and exitthe modular container through holes 8 b and 8 c. The loop shaped pathsfor the fibers and ribbon cables inside of modular container 7 arenecessary to avoid bend radii of less that approximately 1 inch in orderto prevent fiber breakage due to the well known effect of static stressfatigue. Often, the fiber cables are secured in their loop shapes usingtie-wraps or some other convenient mechanism. Typically, the fiberribbon cables are also secured in place at the holes 8 a, 8 b, and 8 cby using a bonding agent such as a low stress epoxy cement or siliconerubber cement to fasten them to the modular container wall where theholes are located.

While the modular container shown in FIG. 2 contains 4 optical taps, itis practical to include additional layers of optical taps so that 8optical taps (2 layers) or 12 optical taps (3 layers) can fit into asingle modular container. Typical outside dimensions for such a modularcontainer are approximately ½ inches by 3 inches by 5 inches. Thesemodular containers typically have a rectangular box shape as shown inFIG. 2 with removable covers. These modular containers are normally madefrom a strong plastic or metal for durability.

FIG. 3 is another example of a modular container. In this instance, themodular container 15, that typically has a rectangular cross-section ofapproximately 3 inches by 5 inches, houses a 1×32 PLC optical splitter10. There is a single input fiber 11 and 32 output fibers that areorganized in four ribbon cables 12 a, 12 b, 12 c, and 12 d containing 8optical fibers each that pass through the wall of the modular containerat holes 13 a, 13 b, 13 c, and 13 d, respectively. There is also asmaller hole 14 in the container wall to pass the single input fiber 11.The splitter and optical fiber cables are secured in place usingtechniques described above for the optical tap.

FIG. 4A shows an exploded view of an HDP equipment enclosure 27 thatreveals 16 modular containers, 15 a through 15 p, that are enclosedwithin. Typical outside dimensions for these modular containers areapproximately ½ inches by 3 inches by 5 inches so that they can fitinside of an equipment enclosure 27 that is rack mountable. There is amultiplicity of 16 MTP or MPO optical connectors on each of the fourconnector blocks 16 a, 16 b, 16 c, and 16 d that are inserted in to thefront panel 17 of the equipment enclosure. The equipment enclosure isformed by securing the front panel 17 and the back panel 18 to the leftand right side plates 19 and 20, respectively, using screws. Theequipment enclosure is completed by securing its bottom plate 21 and topplate 22 in place with screws. The equipment enclosure also hasadjustable brackets 23 and 24 that serve to mount the enclosure intoequipment racks having widths of 19 inches, 21, inches or 23 inches.Convenient handles 25 and 26 are also secured in place using screws.These handles assist in transporting the equipment enclosure and ininserting it into an equipment rack. Normally, equipment enclosures aremade from metal, although other durable materials like fiber glass andboron-graphite fiber composites could also be used if desired. FIGS. 4Band 4C show front and back assembled views, respectively, of the HDPequipment enclosure.

FIG. 5 shows the routing path for the two input fiber ribbon cables(pig-tails) 30 a and 30 h associated with modular containers 15 a and 15h, the two output fiber ribbon cables (pig-tails) 40 a and 40 h, and thetwo tap fiber ribbon cables (pig-tails) 50 a and 50 h also associatedwith modular enclosures 15 a and 15 h. As these ribbon cables exit theirrespective modular containers they are secured in a loop before beingterminated on the connector blocks 16 a, 16 b, 16 c, and 16 d that aremounted on the front panel of the equipment enclosure.

The reason that these particular ribbon cables follow an indirect looppath to the front panel is because it is cost effective to make all ofthe ribbon cables the same length (approximately 30 inches) and topre-terminate them with MTP or MPO optical connectors that can beinserted directly into the front panel of the HDP equipment enclosure. Alooping path has been determined to be the preferred way to positionfiber ribbon cables coming out of the component containers that arelocated near to the front panel so as to minimize the mechanical bendinginduced stresses in the individual fibers. Such a loop is not requiredin the ribbon cables coming out of component containers that are locatedfurther from the front panel. Rather, a more direct path can be usedwith these ribbon cables passing directly down the central channelbetween the two rows of equipment modules. In all cases, it is importantthat any bend radii associated with the paths of the ribbon cables berelatively large (greater than about 1 inch) to avoid fiber breakage dueto the well known mechanism of static stress fatigue.

It is advantageous if the shape of the modular containers has sufficientsymmetry that these modules can be located on either the left-hand orright-hand side of the equipment enclosure with their ribbon cable exitholes directly facing the channel between the two rows of modularcontainers. This strategy avoids the need to inventory two types ofmodular containers that are specifically left-handed and right-handed.

While the above drawings provide representative examples of specificembodiments of the inventive equipment enclosure, there are numerousvariations on the types of optical components contained within theseequipment enclosures, the sizes and number of modular containers and thetypes of optical fiber cables and optical connectors that can be used.

What is claimed is:
 1. An equipment enclosure used in indoor equipmentbays that holds in place within its interior a multiplicity of boxshaped modular containers with outside dimensions of approximately 3inches by 5 inches by ½ inch that are organized in rows and columns andthat may be stacked in multiple layers to efficiently fill the availablespace such that: (a) the optical components in one or more of themodular containers are any combination of optical taps, arrayedwaveguide gratings (AWGs), optical splitters, and/or optical switches,(b) the above optical components are connected with single fiber cableor multi-fiber ribbon cable pig-tails that extend beyond the individualmodular containers and terminate with single-fiber or multi-fiberoptical connectors that are secured on the front panel of the equipmentenclosure, (c) at least two rows of module containers run between thefront and rear panels of the equipment enclosure in which one of the atleast two rows of modular containers is located on the right-hand sideof the equipment enclosure and another row is located on the left-handside of the equipment enclosure, and (d) there is sufficient spacebetween adjacent rows of modular containers to serve as a channel(s) tocontain and guide the multi-fiber ribbon pig-tails emanating from themodular containers so that the pig-tails can be terminated with opticalconnectors on the front panel of the equipment enclosure with minimumbend radii of at least one inch for the entire lengths of the ribbonpigtails.
 2. An equipment enclosure as in claim 1 which has a width,including the width of any mounting brackets, that can fit into and besecured in a standard 19 inch wide equipment rack.
 3. An equipmentenclosure as in claim 2 that fits into a space that is 1 RU (1.75inches) high.
 4. An equipment enclosure as in claim 2 that fits into aspace that is an integer number of RUs (rack units) high.
 5. Anequipment enclosure as in claim 1 which has a width, including the widthof any mounting brackets, that can fit into and be secured in a 21 inchwide equipment rack.
 6. An equipment enclosure as in claim 5 that fitsinto a space that is 1 RU (1.75 inches) high.
 7. An equipment enclosureas in claim 5 that fits into a space that is an integer number of RUs(rack units) high.
 8. An equipment enclosure as in claim 1 which has awidth, including the width of any mounting brackets, that can fit intoand be secured in a 23 inch wide equipment rack.
 9. An equipmentenclosure as in claim 8 that fits into a space that is 1 RU (1.75inches) high.
 10. An equipment enclosure as in claim 8 that fits into aspace that is an integer number of RUs (rack units) high.
 11. Anequipment enclosure as in claim 1 that has different sizes of removablerack mounting brackets that can be selected so that the equipmentenclosure can fit into equipment racks that are either 19 inches, 21inches or 23 inches wide.
 12. An equipment enclosure as in claim 1 inwhich the rows of modular containers are stacked two or more moduleshigh.
 13. An equipment enclosure as in claim 1 having a depth in therange of 19 to 22 inches.
 14. An equipment enclosure as in claim 1having a depth in the range of 12 to 14 inches.
 15. An equipmentenclosure as in claim 1 having a depth in the range of 9 to 11 inches.16. An equipment enclosure as in claim 1 having modular containers thatare made out of plastic.
 17. An equipment enclosure as in claim 1 havingmodular containers that are made out of metal.
 18. An equipmentenclosure as in claim 1 in which the shape of the modular containers hassufficient symmetry that these modules can be located on either theright-hand or left-hand side of the equipment enclosure with theirribbon cable exit holes directly facing the channel between the two rowsof modular containers.
 19. An equipment enclosure as in claim 1 in whichthe optical fiber connectors mounted on the front panel are single-modefiber connectors compatible with the MTP or MPO types.
 20. An equipmentenclosure as in claim 1 in which all of the single fiber cable ormulti-fiber ribbon cable pig-tails extend beyond the individual modularcontainers for approximately 30 inches and terminate with single-fiberor multi-fiber optical connectors that are secured on the front panel ofthe equipment enclosure.